Pneumatically operated mold ejection apparatus

ABSTRACT

A pneumatically operated mold ejection apparatus using a pneumatic pressure source exterior to a multiplate injection molding tool. The pressure source operates at least one knock-out pin disposed within a molding plate. Said pin is connected to a pneumatic piston spring loaded against a stop positioning the pin flush with the inner wall of the cavity during injection of plastic. The stop also positions the piston so that compressed air can reach the piston&#39;s surface when the pressure source is actuated. The piston includes a circumferential annular groove containing an O-ring for pneumatic sealing. The back side of the molding plate includes pneumatic channels between the cylinder and their intersection with a complimentary channel in the backing plate. These channels connect the system to the pressure source, and are surrounded by an O-ring trapped between the molding and backing plates for pneumatic sealing.

FIELD OF THE INVENTION

The present invention relates primarily to the field of injectionmolding using multiplate molds with replaceable core and cavity platesthat may be of a multicavity structure. It will be described in respectto injection molding, but the invention applies to related fields aswell, including especially compression molding, structural foam moldingand reaction injection molding. More particularly, the invention relatesto an apparatus to facilitate ejection of the workpieces from the moldregardless of the positioning of the cavities as the core and cavityplates are changed. It further relates to the method of repositioningthe ejection apparatus to accommodate the repositioned cavities withoutdrilling a plurality of holes through the backing plates of the mold asis presently practiced in the art.

BACKGROUND OF THE INVENTION

Injection molding of many products is a practical, efficient andeconomical fabrication technique for many plastic articles and parts.Injection molding apparatus generally includes a mold formed of twoportions, one of which is a cavity and the other a core which togethercorrespond to the part being molded. The plastic or other material ofwhich the article or part is fabricated is melted and mixed and theninjected into the mold, following which the two portions of the mold areopened to eject the finished part referred to hereinafter as theworkpiece. The equipment is designed to open and close the mold portionsand of course they are held tightly together in appropriate alignmentduring the molding process. Usually one portion of the mold is held infixed position while the other portion is movable to permit ejection ofthe workpiece.

The economies of injection molding are only achieved, however, if thevolume of articles or parts is such to justify the set-up costs,including design and creation of the tooling. A change in any feature ofa molded part must either be machined into what the mold is alreadyproducing, i.e, machined on the article itself rather than the mold,destroying much of the economies of injection molding, or the tool(mold) must be revised or replaced at substantial cost.

It is for that reason that replaceable cavity and core portions of moldshave been developed. An excellent example of this is the apparatus ofTaketa, U.S. Pat. No. 3,871,611 which contains a lucid disclosure onthis technique. Further, the use of replaceable cavity and core portionsof a mold is facilitated by the use of multiplate molds, which are alsoknown in the art. Examples of multiplate molds are taught by Diehl, U.S.Pat. No. 3,892,512 and by Carlin, U.S. Pat. No. 3,327,355.

These and similar devices known in the art allow the costs of certaintooling changes to be reduced by replacement only of the core and cavityportions of the mold. Indeed, for some short run items, the core andcavity portions can be made of softer material that is easier and lessexpensive to machine, such as aluminum. This is because the core andcavity plates are reinforced by backing plates that may be made frommore durable and rigid material such as steel.

Injection molding includes a requirement for effective removal of theworkpiece from the mold cavity when the mold is opened so the mold canbe recycled to produce a new workpiece. The apparatus and methodsconventionally used in the injection molding art to eject the workpiecefrom the mold include knock-out pins and gas pressure applied directlyto the workpiece. Knock-out pins have frequently involved mechanicallymoved or hydraulically pressurized operators. Of course, the knock-outpins must be properly positioned in regard to the cavity to achievetheir purpose of removing the workpiece without damaging same. Whenmultiplate molds or tools are used, with various different cavitylocations, repeated relocation of the knock-out pins has historicallynecessitated drilling through the backing plates so often that they canbegin to look like a swiss cheese and must be replaced. Furthermore,mechanically operated knock-out pins which are actuated using an ejectorplate movable within an ejector box, must be located to avoid coolingwater lines in the backing plate. Gas pressure or blow-out ejectiondevices suffer from the disadvantage that the orifice necessarily formedwithin the inner wall of the mold cavity frequently becomes plugged witha plastic or other material from which the workpiece is made. Thisdifficulty with blow-out devices is well documented in the prior artherein described.

The present invention provides an apparatus that overcomes both of theseforegoing disadvantages of the prior art by using a pneumaticallyactuated knock-out pin whose structure is entirely disposed within oneor both molding plates. These are the portions of a multiplate mold thatare retooled anyway for any design changes. Pneumatic channels within,but on the surface of, the molding plate bring the pressure source towherever the knock-out pin should be disposed for best effectiveness.

Because a pneumatically pressurized knock-out pin utilizes a pistonoperator, a pre-examination search commissioned by the inventor of thepresent invention revealed a variety of prior art references dealingwith knock-out devices, pneumatics, piston operators and the like. Mostof this prior art is of modest relevance to the disclosure, but isrecited for whatever background is obtainable therefrom.

For example, Schneider, U.S. Pat. No. 3,952,991 teaches a type ofknock-out device that uses a piston as a valve rather than as theoperator itself. It is really a type of blow-out device, and thisreference also parenthetically discloses a use of a piston as a valvefor flow of plastic or the like during the portion of the molding cyclewhen injection is not occurring. Another type of blow-out device istaught by Sheffield, et al., U.S. Pat. No. 4,653,997, which utilizesmiltiple ports and a retractable port to assist removal of a lightweightworkpiece such as a plastic cup. No pneumatically pressurized pistonapplies knock-out force to the workpiece in this reference.

Other pneumatically operated knock-out devices are those taught byHujik, U.S. Pat. No. 3,914,086 which discloses a pneumatic pistonoperator with a custom shaped head for a particularized product. Seealso Dromigny, et al., U.S. Pat. No. 4,686,076 which uses a pistonactuator in conjunction with an injection mold to hold a preprinted filmin place in the mold to combine the film with the material from whichthe workpiece is fabricated.

Bearing in mind the foregoing, it is a principal object of the inventionto provide an ejection apparatus for use with a multiplate mold, thestructure of which is disposed entirely within a replaceable moldingplate, usually the cavity plate.

A related object of the invention is to permit the ejection apparatus tobe relocated as design changes are made without making changes to thebacking plates or any other exterior surface of the mold.

A further object of the invention is to utilize a pneumatic operator forthe ejection apparatus as an economical source of force that can bereadily introduced into the mold and easily controlled from the moldexterior.

Another object of the invention is to utilize knock-out pins which canbe machined to close tolerances with a bore in which they move axiallyto prevent leakage of the plastic or other molding material into theejection apparatus.

An additional object of the invention is to utilize a compact apparatusfor ejection so that as many knock-out pins can be positioned at optimallocations within a molding plate as are needed to optimize efficientejection of the workpiece from the molding surface or cavity withoutdamaging same.

An allied object of the invention is to use ejection apparatus ofstandardized configuration so that the apparatus will be interchangeablewith a plurality of locations in each of a plurality of molding sites ina multicavity tool and also between a plurality of different moldingplates.

A further object of the invention is to utilize an apparatus forejection from an ejection molding multiplate tool that is appropriatefor use with a molding plate that may be made from an easily machinedmaterial such as aluminum to economize on tooling changes for short runarticles or parts.

Also an object of the invention is to provide a method for ejection ofworkpieces from a multiplate injection molding tool which can berepositioned economically as tooling changes are made within the moldingplates.

A further object of the invention is to provide a method for ejection ofa workpiece from a multiplate mold wherein repositioning can be achievedentirely within the molding plate.

A related object of the invention is to provide a method thatfacilitates repositioning of knock-out apparatus.

An additional object of the invention is to utilize a pressure (power)source external of the mold whose control and adjustment are easily andeconomically achieved.

A collateral object of the invention is to utilize a pressure sourcewhich, when introduced within the exterior surface of the mold will beharmless if the same leaks from the path to which it is directed.

An allied object of the invention is to utilize a pressure source which,when introduced into the mold can be directed without expensivefittings, piping, such as is necessary if the force were derived usinghydraulic fluid to move an ejector plate as is known in the art.

Other objects and advantages of the present invention will be apparentto those skilled in the art upon reference to the following descriptionsand the appended drawings.

SUMMARY OF THE INVENTION

In accordance with a principal aspect of the invention there is providedpneumatically operated mold ejection apparatus using a pneumaticpressure source of conventional means exterior to a multiplate tool,which pressure source is selectively activated using the mold cycle tooperate at least one knock-out pin disposed within the molding plateusually the cavity plate. The knock-out pin is connected to a pistonthat is urged by biasing means to a stop such that the knock-out pin ispositioned flush with the inner wall of the molding surface or cavityduring the injection of plastic or other molding material into the tool.The stop also positions the piston so that gas, normally compressed air,can enter into the cylinder to bear upon the piston surface when theexternal pneumatic pressure source is selectively actuated. The pistonpreferably has about its circumference an annular groove in which isdisposed a cylinder O-ring to optimize pneumatic sealing between thecircumference of the piston and the inside diameter of a bushing thatpreferably forms the cylinder walls.

The side of the molding plate opposite the molding surface ischaracterized by at least one pneumatic channel between the cylinder andan intersection with a complimentary pneumatic channel in the backingplate. The latter is perforated by a pneumatic orifice which in turn isconnected to the external pneumatic pressure source and valving andregulating means for control and selective actuation of the system. THepneumatic channel of the molding plate is surrounded by a perimetergroove in which is disposed a perimeter O-ring to optimize sealingagainst leakage of the compressed air from between the molding plate andthe adjacent backing plate. Thus, fluid communication is establishedfrom the external pneumatic pressure source through the valve, whichselectively actuates it, to the pneumatic orifice into the tool, andthence through the complimentary pneumatic channel and molding platepneumatic channel to the piston. Therefore, when the external pneumaticpressure source is actuated at the proper time in the mold cycle, fluidcommunication to the piston results in a force opposite that of thebiasing means to move the knock-out pin from its position flush with theinterior surface of the molding surface or cavity and against theworkpiece to eject the same from the molding surface or cavity when themold is opened. Incidentally, the biasing means is preferably a coilspring mounted on the shaft of the knock-out pin, but any biasing meansmay be used, including reversing pressure in the pneumatic system.

The apparatus is designed so that the pneumatic orifice andcomplimentary pneumatic channel, which are disposed in a backing plate,provide a pressure source for as many or as few of the knock-out pins asare needed in a molding plate and at any location. The perimeter grooveand perimeter O-ring are also disposed in the backing plate and simplysurround the area in the adjacent molding cavity plate where anyknock-out pins could possible be desired. As will be seen from thefollowing detailed descriptions and upon reference to the drawings,optimum use of this concept may result in the selection of more than onepneumatic orifice, complimentary pneumatic channel and perimeter grooveand O-ring although that decision, once made, cannot be changed soreadily as the changes in the cavity and core (molding) plates asdescribed above. The most likely reason for a plurality of pneumaticorifices, complimentary pneumatic channels and perimeter grooves andO-rings is that the cavity plate and core plate can be divided into aplurality of same to increase the flexibility and the molding of anumber of short run articles or parts.

In accordance with another major aspect of the invention, there isprovided a method for the relocation of injection molding workpieceejection means within a multiplate mold having replaceable core andcavity plates. The method contemplates the use of relocatable pneumaticcylinders containing actuating pistons and a series of pneumaticchannels all of which are disposed within the molding plates. The methodalso contemplates a pneumatic pressure source, valving and control meansof conventional design for selective actuation of the apparatus and theplacement of at least one pneumatic orifice and the accompanyingcomplimentary pneumatic channel surrounded by a perimeter groove andO-ring in a backing plate.

With this as a starting point, the inventive method contemplates theplacement of at least one knock-out pin in a molding plate which isusually a cavity plate. The knock-out pin connects to a piston which isdisposed within cylinder walls formed by a bushing placed in a hole stepdrilled in the side of the molding plate opposite the molding surface.Prior to assembly of the cavity plate to the cavity backing plate, theknock-out pin, piston with annular grooves and cylinder O-rings andbiasing means in the form of a coil spring are placed within a bushingand held with a snap ring retainer to form a completed pneumaticcylinder and knock-out pin mechanism. The snap ring retainer fits in agroove machined in the inside of the bushing.

Also prior to assembly of the molding plate and backing plate, pneumaticchannels are machined into the back of the molding plate to providefluid communication between the pneumatic orifice and the pneumaticcylinder through the pneumatic channel and complimentary pneumaticchannel when assembly is completed. Of course, as many of thesepneumatic cylinder knock-out pin mechanisms can be utilized as desiredsince they are simply placed into the back of the molding plate and thepneumatic channels are machined to interconnect them with the pneumaticpressure source. This procedure can be relatively inexpensive, becausethe molding plate for short run articles or parts can be fabricated froman easy-to-machine material such as aluminum.

In accordance with a consequent aspect of the invention, the method isprovided for utilization in actual molding practice of theabove-described apparatus and method of assembly to actually ejectworkpieces from cavities in a multiplate injection molding tool when thesame is opened. A convention pneumatic pressure source is connectedupstream of a pressure regulator and valve, which valve is actuated byreference to the cycle of the injection molding machine at a time whenejection of the workpiece from the mold cavity is desired. Whenactuated, the valve opens and pneumatic pressure passes through at leastone pneumatic orifice and into a complimentary pneumatic channel, bothof which have previously been machined into the backing plate. Then thepneumatic pressure passes from an intersection between the complimentarypneumatic channel to the pneumatic channel or a plurality of samedisposed in the back of the molding plate.

Excessive leakage of pneumatic pressure is prevented by the combinationwhen assembled of the cavity backing plate, cavity plate, and perimeterO-ring disposed in a perimeter groove surrounding the intersection ofall pneumatic channels and complimentary pneumatic channel. Thepneumatic pressure then passes from the pneumatic channel to theoperating surface of the pneumatic piston disposed within cylinder wallsformed by the bushing. Sealing between the piston working surface andthe inside diameter bushing or cylinder wall is achieved using thecylinder O-ring disposed with an annular groove around the pistonworking surface. Once the pneumatic pressure has reached the workingsurface of the pneumatic cylinder, a force is exerted thereon depressingthe biasing means in the form of a coil spring and moving the knock-outpin out from the molding surface or the mold cavity to eject theworkpiece therefrom.

The invention will be better understood upon reference to the followingdetailed description and the drawings in which:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of an assembled multiplate mold or tool ofthe type employed in the present invention.

FIG. 2 is a cross-section view taken through the multiplate tool of FIG.1 through the line 2--2 thereof.

FIG. 3 is a top perspective exploded view of a multiplate tool showingsome of the internal features of the present invention.

FIG. 4 is a bottom perspective view of the same multiplate mold andillustrating other of the features of the present invention.

FIG. 5 is an enlarged bottom perspective exploded view of the pneumaticcylinder seen in assembled form as part of the center portion of FIG. 4.

FIG. 6 is an enlarged fragmentary cross-section view of the pneumaticcylinder and knock-out pin mechanism shown in exploded view in FIG. 5and is the first of four such views illustrating the operation of thismechanism. In this figure, the mold and mechanism are shown in assembledform prior to injection of the plastic or other molding material intothe mold, with a knock-out pin flush with the interior surface of themold cavity.

FIG. 7 is also an enlarged fragmentary cross-section view of thepneumatic cylinder and knock-out pin mechanism with the cavity havingbeen filled by the injection of plastic or other molding material.

FIG. 8 is another enlarged fragmentary cross-section view showing thecore plate or clamp opened preliminary to ejection of the workpiece fromthe cavity in the mold.

FIG. 9 is the final enlarged fragmentary cross-section view illustratinguse of the pneumatic cylinder and knock-out pin mechanism ejecting theworkpiece from the cavity in the mold and showing the coil springbiasing means compressed as a consequence of the pneumatic pressureapplied to the working surface of the piston.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a perspective view of the principal portions of anassembled multiplate mold or tool 2 which is adapted for use in themanner of the invention. It shows a cooling inlet 4 for the core backingplate 10 and cooling inlet 5 for the cavity backing plate 40 which issometimes referred to in the trade as the clamp side. The core backingplate 10 is also referred to in the trade as the hot side and thecooling outlet 6 is on the far side thereof. The sprue port 7 is shownon the upper surface thereof. The sprue port is the point at whichplastic or other molding material is injected into the mold using theinjection molding machine. The injection molding machine is of aconventional type and is not shown. The sprue port 7 is shown surroundedby the exterior of the sprue bushing 11. Shown sandwiched between thecore backing plate 10 and the cavity backing plate 40 are the core plate20 and cavity plate 30. On the cavity backing plate 40 are shownpneumatic inlets 8 and 9. The cavity plate 30 is shown in optional splitform 31 and 32 separated by T-bar 33 which is also used to hold 31 and32 to cavity backing plate 40.

Turning now to FIG. 2, a cross-sectional view taken through the line2--2 of FIG. 1 shows the multiplate tool 2 in assembled form with corebacking plate 10 on top of core plate 20 which is, in turn, on top ofcavity plate 30. At the bottom of the stack is cavity backing plate 40.At this point it should be noted that core plate 20 is not shown with acore profile, having a substantially planar surface in proximity to thefirst cavity 34. The reason is that the particular product first madeusing the invention is a flat profile part using a textured surface.Thus the mold aspects of core plate 20, textured surface 22, in theillustrated example, simply provides texturing to the part, but theinvention disclosed is no less applicable to the normal situation whereboth a core and cavity are utilized, and placing of knock-out pins inthe core plate with analogous changes to the core backing plate as tothose in the cavity backing plate are obviously contemplated althoughnot specifically described for the application shown. It is for thisreason that the generalized terms molding plate and molding surface aremostly used in the application in lieu of the more specific cavity plateand cavity.

FIG. 2 also illustrates sprue port 7, of sprue 12 which is disposedwithin sprue bushing 11. Also disclosed in sprue knock-out 14.

Also disposed within cavity plate 30 is pneumatic cylinder and knock-outpin mechanism 50, which will be more fully described in connection withother figures. A pneumatic pressure source external to the mold, and ofconventional design, selectively applies pressure to the interior of themold through pneumatic inlet 8 which may be threaded at 16 to achieve asubstantially pressure tight connection between pneumatic orifice 65 andthe external pneumatic pressure source, now shown. There is then fluidcommunication between the external pneumatic pressure source throughpneumatic inlet 8 and pneumatic orifice 65 and intersectingcomplimentary pneumatic channel 64 and thence through pneumatic channel62 to pneumatic cylinder and knock-out pin mechanism 50.

FIG. 3 shows three of the four plates in multiplate mold 2 in anexploded configuration to illustrate the internal features of thepresent invention. In this view, core backing plate 10 and core plate20, which in this example is a texture plate, remain assembled to eachother notwithstanding the exploded configuration in the remainder of thefigure. It will be seen in this figure also that core plate 20 has beendivided into two portions 21 and 23 corresponding to the two portions 31and 32 of the cavity plate, which are held in place and separated byT-bar 33. It will be seen that cavity plate 30, really divided intocavity plates 31 and 32 is a multicavity plate having a first cavity 34and a second cavity 36. When the mold is in operation, plastic or othermolding material is injected from the injection molding machine throughthe sprue port 7 until it reaches the cavity plate 30 at which point theflow is divided along runner 38 to the two cavities 34 and 36. In eachof these cavities, knock-out pins 51 can be seen.

Cavity backing plate 40, referred to in the trade sometimes as the clampside, has pneumatic inlets 8 and 9 which are in fluid communication withpneumatic orifice 65 and complimentary pneumatic channel 64. There isalso machined in the upper surface of cavity backing plate 40 aperimeter groove 61 in which is disposed a perimeter O-ring 60. Theperimeter O-ring 60 is pressed between cavity plate 30 and cavitybacking plate 40 when they are assembled to minimize leakage ofcompressed air used to control knockout pins 51.

In FIG. 4 the underside of the core plate 20 and cavity plate 30 can beseen. As noted previously, the core plate in this instance does not havea profile, but is of a planar configuration although there is nointention to limit the present invention thereby. Core plate 20 includesa textured surface 22 which is what is desired for the particular partsin question. Sprue bushing 11 and sprue 12 are also visible, and coreplate 20 is shown split, 21 and 23 correspond to cavity plates 31 and 32separated by T-bar 33. On the underside of cavity plate 30 can be seenpneumatic channels 62 which intersect with complimentary pneumaticchannel 64 as shown in FIG. 3. Note that pneumatic channels 62 are alldisposed within the area surrounded by perimeter O-ring 60. Also, seenare pneumatic cylinder and knock-out pin mechanism 50 which will be morefully described hereinafter in regard to FIG. 5, etc.

FIG. 5 is an enlarged exploded view of pneumatic cylinder and knock-outpin mechanism 50 that includes knock-out pin 51, coil spring 59, pistonsurface 57, snap ring retainer 58, etc. Disposed about the pistonsurface 57 is an annular groove 53 in which is placed a cylinder O-ring55. Offset or raised from piston surface 57 is a base flat 56 whosepurpose will be described in regard to subsequent figures. Whenassembled, these parts form a pneumatic cylinder 52 when disposed withinbushing 54. They are held in position during assembly of the mold platesby placement of snap ring retainer 58 in snap ring groove 46, which hasbeen machined in bushing 54. Also seen machined in the underside ofcavity plate 30 is pneumatic channel 62 which supplies air pressure topiston surface 57 through the complimentary pneumatic channel 64 as seenin FIG. 3. Knock-out pin 51 closely fits within the bore 48, the edge ofwhich is seen in FIG. 5.

FIG. 6 is an enlarged fragmentary cross-section view showing thepneumatic cylinder and knock-out pin mechanism 50 in assembled form andwith the took closed prior to injection of the injection of the plasticor other molding material. That is cavity 34 is empty but core plate 20is in close proximity to cavity plate 30. Knock-out pin 51 is in closefitting relationship to bore 48 the edge of which can be seen in thisfigure. The effect is to minimize leakage of the plastic or othermolding material from the cavity into the pneumatic cylinder andknock-out pin mechanism 50.

FIG. 7 is also an enlarged fragmentary cross-section view of theknock-out pin mechanism 50 with the cavity 34 having been filled by theinjection of plastic or other molding material 35. It will be seen thatknock-out pin 51 remains flush with the floor of cavity 34 the uppersurface of which forms a part of the cavity. In fact, pneumatic cylinderand knock-out pin mechanism 50 remains positioned as it was in FIG. 6.The precise location of knock-out pin 51 flush with the inside surfaceor floor of cavity 34 is accomplished by the fact that base flat 56rests firmly on cavity backing plate 40. It is expressly not dependenton the position of snap ring retainer 58 which is disposed within thesnap ring groove 46 which has been machined into the inside surface ofbushing 54. This fact can be seen from reference to the air gap existingat 44 between the upper surface of snap ring retainer 58 and pistonsurface 57. This is because snap ring retainers do not provide nearly asprecise a location for the top of knock-out pin 51 as can beaccomplished using base flat 56 resting upon cavity backing plate 40.

FIG. 8 is a further enlarged fragmentary cross-section view of thepneumatic cylinder and knockout pin mechanism 50. The positioningthereof remains as shown in FIGS. 6 and 7, the main purpose of FIG. 8being to illustrate that core plate 20 has been retracted as the mold isopened so that the plastic molded workpiece 37 can be removed using theprocedure shown in FIG. 9. Before proceeding to FIG. 9, however, it isuseful to note that base flat 56 is held firmly on cavity backing plate40 using biasing means preferably in the form of coil spring 59. Thisbiasing means also serves to return knock-out pin 51 to its positionflush with the floor of cavity 34 after the same has been utilized asshown in FIG. 9, but alternative biasing means can be employed toachieve the same result. Pneumatic sealing is maximized by cylinderO-ring 55 disposed within annular groove 53. The external circumferenceof cylinder O-ring 55 bears on the interior cylinder wall formed bybushing 54. Piston surface 57 is separated from cavity backing plate 40using base flat 56 to allow compressed air to enter into pneumaticcylinder 52 from pneumatic channel 62, which in turn is in fluidcommunication with the external pressure source above-described.

Turning finally to FIG. 9, the objective of ejection of workpiece 37 isaccomplished using pneumatic cylinder and knockout pin mechanism 50.Compressed air has entered pneumatic cylinder 52 through pneumaticchannel 62 and is thus applying a sufficient force on piston surface 57to compress coil spring 59, raise knock-out pin 51 and move workpiece 37from within cavity 34. Core plate 20 remains retracted so that workpiece37 can be removed from the tool.

In addition to the apparatus described and the method by which the sameis operated, the invention contemplates a method by which cavities canbe changed and moved, and more particularly, knock-out pins can bereadily relocated to accommodate tooling changes for short run articlesand parts. The method generally comprises the following steps:

1. Determining the size and shape of the cavity and core to injectionmold the product and placement of the same within the body of amultiplate tool.

2. Machining of the core and cavity portions of the core and cavityplates in a multiplate tool that will form the article or part.

3. Establishing appropriate locations for knock-out pins.

4. Calculating the appropriate height of a knock-out pin such that thedistance between a base flat surface and the top of the knock-out pinwill coincide exactly with the distance between the upper surface of acavity backing plate and the molding surface of the molding plate at thelocation of each given knock-out pin.

5. Machining the knock-out pin to the length so established.

6. Boring the bottom of the molding plate to the correct diameter forthe insertion of the knock-out pin in the location desired.

7. Step drilling in concentric manner the rear of the molding plate forthe placement of a bushing forming the circumference of a pneumaticcylinder.

8. Machining a pneumatic channel into the rear of the molding plate toaccomplish fluid communication between the site of the pneumaticcylinder and an intersection between a complimentary pneumatic channelpreviously placed in the interior surface of the backing plate.

9. Press fitting bushings into the locations drilled into the rear ofthe molding plate to form the circumference of the pneumatic cylinder.

10. Placing a coil spring on the shaft of a knock-out pin.

11. Placing a cylinder O-ring in an annular groove around a pistonsurface attached to the knock-out pin.

12. Inserting a knock-out pin into the bore previously disposed in thecavity plate to a sufficient depth for the following step.

13. Inserting a snap ring retainer into a snap ring groove previouslymachined in the inside diameter of the bushing.

14. Repeating the foregoing procedure for as many locations asdetermined above in step 3 for each of the knock-out pins desired.

15. Assembling the tool with a perimeter O-ring between molding plateand adjacent backing plate placed in a perimeter groove previouslymachined in the backing plate and surrounding the pneumatic channel andcomplimentary pneumatic channel.

While the invention has been described in connection with a preferredembodiment in regard to injection molding, it will be understood thatthere is no intention to thereby limit the invention. On the contrary,there is intended to be covered all alternatives, modifications andequivalents as may be included within the spirit and scope of theinvention as defined by appended claims, which are the sole definitionas the invention. Application thereof to the fields of compressionmolding, structural foam molding and reaction injection molding isspecifically within the contemplation of the inventor.

What is claimed is:
 1. In an improved multiplate multicavity moldingtool having molding plates comprising a cavity plate and a core plate,backing plates comprising a cavity backing plate and a core backingplate, all taken in combination with an external pneumatic pressuresource and accompanying pressure level and valving controls keyed toselectively actuate when the tool is opened to eject workpieces usingknock-out pins, the improvement comprising:for each said knock-out pin,a pneumatic piston disposed within and movable along an axis of acylindrical opening machined into a said molding plate on a sideopposite a molding surface thereof and forming a pneumatic cylinderthereby, said piston being connected to each said knock-out pin; a stopin proximity to each pneumatic piston to accurately position eachknock-out pin such that a portion thereof that contacts the workpieceadjacent said knock-out pin conforms with minimal surface discontinuityto the molding surface; a biasing means disposed in physicalcommunication with each pneumatic piston to both hold said piston firmlyagainst the stop and to return said piston to the stop when theknock-out pin has been moved to eject the adjacent workpiece from themolding surface; a pneumatic orifice spaced from each said cylindricalopening, penetrating at least one of the backing plates and in fluidcommunication with the external pneumatic pressure source; acomplimentary pneumatic channel spaced from each said cylindricalopening in fluid communication with the pneumatic orifice and disposedwith the backing plate that the pneumatic orifice penetrates; and apneumatic channel disposed within said molding plate extending from saidcomplimentary pneumatic channel to each said cylindrical opening toestablish fluid communication through the pneumatic orifice andcomplimentary pneumatic channel between the external pneumatic pressuresource and each pneumatic piston in said molding plate.
 2. The tool ofclaim 1 in which the molding plate is said cavity plate and the moldingsurface is a cavity.
 3. The tool of claim 1 in which the molding plateis said core plate and the molding surface is a core.
 4. The tool ofclaim 1 in which the molding plate is said core plate and the moldingsurface is a substantially planar textured surface.
 5. The tool of claim1 in which the pneumatic cylinder is further comprised of a bushingpress fitted into the cylindrical opening machined into the moldingplate, said bushing having an interior surface that forms a pneumaticcylinder wall in proximity to the pneumatic piston.
 6. The tool of claim1 in which the pneumatic piston is further comprised of an annulargroove disposed about a circumference of a piston surface against whichcompressed gas bears, and a cylinder O-ring is disposed within theannular groove, said cylinder O-ring maximizing a pneumatic seal betweenthe pneumatic piston and the cylindrical opening in which the pneumaticpiston is disposed.
 7. The tool of claim 1 in which the stop iscomprised of a base flat raised from a piston surface against whichcompressed gas bears, said base flat coming in firm contact with saidbacking plate to which the molding plate is attached, thereby accuratelypositioning the knock-out pin to which the pneumatic piston isconnected.
 8. The tool of claim 1 in which the biasing means is a coilspring disposed about a shaft of the knock-out pin.
 9. The tool of claim1 which further comprises a perimeter groove machined into a backingplate surface that contacts said molding plate, and a perimeter O-ringis disposed within the perimeter groove to maximize a pneumatic sealcircumscribing the pneumatic orifice and the pneumatic channel betweenthe backing plate and the molding plate.
 10. The tool of claim 1 inwhich molding plates are divided into a plurality of same and adjoiningmolding plates are held against bending pressure exerted thereon bycompressed gas in the pneumatic channel using a T-bar bolted to thebacking plate and confining adjacent edges of the adjoining moldingplates.